Chords in a Key
Select any key to instantly see its diatonic chords, Roman numerals, chord qualities, and common progressions.
Diatonic Chords in C Major
Common Progressions in C Major
What Are the Chords in a Key?
Every major key has seven diatonic chords, one built on each scale degree. These are the chords that "belong" to the key and naturally sound good together. The pattern of chord qualities is always the same: major (I), minor (ii), minor (iii), major (IV), major (V), minor (vi), diminished (vii°). So in the key of G: G major, A minor, B minor, C major, D major, E minor, F♯ diminished. Knowing these chords is the foundation of songwriting and chord progression analysis.
Roman Numerals in Music Theory
Roman numerals describe chord functions independently of key. Uppercase (I, IV, V) indicates a major chord; lowercase (ii, iii, vi) indicates a minor chord; vii° indicates a diminished chord. A I–V–vi–IV progression in G is G–D–Em–C. The same progression in C is C–G–Am–F. The Roman numeral notation lets you recognize the same harmonic pattern regardless of what key you're in, which is why it's the universal language of chord analysis.
How to Use Diatonic Chords in Songwriting
When writing a song, starting with the seven diatonic chords of your chosen key gives you a set of chords that are guaranteed to sound harmonically cohesive. From there, you can build progressions by picking chords that create tension and resolution. The V chord always wants to resolve back to I, while the IV chord adds movement and contrast. Once you know which chords belong to a key, you can also spot when a song borrows from outside it, which adds color and surprise. For a visual way to see how keys relate to each other and share chords, explore the circle of fifths.
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